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Tutorial 7: WebApp Layer Vector Tiles

Introduction​

This tutorial demonstrates how to load a tiled CSV Point geometry file into a web application using asynchronous loading, convert it to an SVGMap DOM using the SVGMap framework library, and then display it.

Source Code​

  • Source code directory
  • tiling1.html: Loading of related libraries (SVGMapGIS)
  • Container.svg: Setting up clickable layering ( almost the same as Tutorial 6)
  • simpleTiling.svg: Almost identical to webApp tutorial 6, which manipulates layers with a UI.
  • simpleTiling.html:
  • simpleTiling.js:
    • Reading GeoJSON is the same as in Tutorial 6.
    • Dynamically load GeoJSON based on the display area.
      • When displaying a small scale (wide area), if too many tiles need to be loaded, the loading process will stop and the tiles will not be displayed.

Tutorial​

This approach avoids using dynamic mechanisms like a DBMS in the backend, instead tiling relatively large vector data (in this case, point geometry data) to create content that can be comfortably used as a WebMap/GIS. This type of design is called vector tiling in the GIS world, but it's more commonly known as a Jamstack pattern.

Note​

Furthermore, SVGMap.js can implement tiling for larger datasets that are not possible with other frameworks, or that would normally require connecting to a DBMS to achieve more efficient distribution. For example, this can be easily achieved using SVGMapTools. SVGMap possesses characteristics that allow for a wider application of the Jamstack pattern.

Format of Tiled CSV Data​

  • Both latitude and longitude are divided into 1-degree x 1-degree tiles.
    • tile_[longitude]_[latitude].csv

Example data (tile_125_24.csv)​

X,Y,P27_001,P27_002,P27_003,P27_004,P27_005,P27_006,P27_007,P27_008,P27_009 
125.317688,24.796933,47214,3,03002,03002,Miyakojima City Museum,1166-287 Higashi Nakasonezoe, Hirara,3,-99,1989 
125.282787,24.806925,47214,3,03003,03003,Miyakojima City Hirara Library North Branch,42 Higashi Nakasonezoe, Hirara,3,-99,9999 
125.393222,24.753839,47214,3,03003,03003,Miyakojima City Gusukube Library, 377-1,3,-99,9999 
Miyakojima City Hirara Library, 187,3,-99,9999 Hirara Library, 187,3,-99,9999 
Sarahama Sports Center, 248-1,3,3,9999 
125.195077,24.83307,47214,3,99999,03104,Irabu Sports Park, Irabu-aza Maezatozoe 945,4,3,9999 
125.325478,24.740085,47214,3,99999,03109,Ueno Gymnasium, Ueno-aza Miyakuni 1746-2,4,3,9999 
125.387054,24.756012,47214,3,99999,03129,Gusukube Training Center, Gusukube-aza Fukusato 579,4,3,9999 
125.299712,24.803737,47214,3,99999,03109,Miyakojima City General Gymnasium,676-1 Higashinakasone, Hirara,4,3,9999 
125.328061,24.758818,47214,3,99999,03104,Otake Castle Ruins Park Multipurpose Plaza,1190-134 Nohara, Ueno,4,3,9999 
125.405059,24.764564,47214,3,99999,03104,Gusukube Sports Park Multipurpose Plaza,245-1 Fukusato, Gusukube,4,3,9999 
125.407091,24.764468,47214,3,99999,03102, Gusukube Sports Park Multipurpose Field, 245-1 Fukusato, Gusukube, 4,3,9999 
125.404346,24.76409,47214,3,99999,03115, Gusukube Sports Park Multipurpose Field, 245-1 Fukusato, Gusukube, 4,3,9999 
125.281412,24.729776,47214,3,99999,03102, Shimoji Park (Multipurpose Field), 1590 Yonaha, Shimoji, 4,3,9999 
125.280271,24.730391,47214,3,99999,03104,Shimoji Park (Multipurpose Plaza),Shimoji Yonaha 1590,4,3,9999 
125.263557,24.735081,47214,3,99999,03104,Fureai no Maehama Plaza,Shimoji Yonaha 1199-1,4,3,9999 
125.299657,24.801104,47214,3,99999,03101,Miyakojima City Athletics Stadium,Hirara Higashi Nakasone 935-1,3,3,9999 
125.301632,24.805759,47214,3,99999,03102,Miyakojima City Citizens' Baseball Stadium, Hirara Aza Nishinakasone 1574-1,3,3,9999 
125.301437,24.804417,47214,3,99999,03104,Maefuku Multipurpose Indoor Gymnasium, Hirara Aza Nishinakasone 1574-7,3,3,9999 
125.302217,24.804102,47214,3,99999,03102,Multipurpose Maefuku Sports Ground, Hirara Aza Nishinakasone,3,3,9999 
125.302178,24.803613,47214,3,99999,03104,Multipurpose Maefuku Sports Ground, Hirara-aza Nishinakasone,3,3,9999 
125.389757,24.75579,47214,3,99999,03101,Gusukube Athletic Stadium, Gusukube-aza Fukusato 616,3,3,9999 
125.283694,24.729841,47214,3,99999,03101,Shimoji Athletic Stadium, Shimoji-aza Yonaha 1590,3,3,9999 
125.282256,24.729096,47214,3,99999,03109,Shimoji Gymnasium,Shimoji Yonaha 1590,3,3,9999 
125.326167,24.740636,47214,3,99999,03101,Ueno Athletic Stadium,Ueno Miyakuni 1746-2,3,3,9999 
125.162675,24.835657,47214,3,99999,03109,Irabu Workers' Gymnasium,Irabu Nagahama 1542-5,3,3,9999 
125.161233,24.835137,47214,3,99999,03109,Irabu B&G Marine Center,Irabu-aza Nagahama 1822-5,3,3,9999 
125.161328,24.834684,47214,3,99999,03106,Irabu B&G Marine Center,Irabu-aza Nagahama 1822-5,3,3,9999 
125.262975,24.734973,47214,3,99999,03148,Yonaha Maehama,Shimoji Yonaha 1199-1,3,3,9999 
125.271057,24.802628,47214,3,99999,03148,Painagama,Hirara Shimosato 338-3,3,3,9999 
125.443114,24.74628,47214,3,99999,03148,Aragusuku Coast,Shirobe Aza Aragusuku,3,3,9999 
125.447629,24.741724,47214,3,99999,03148,Yoshino Coast,Shirobe Bora,3,3,9999 
125.432329,24.729739,47214,3,99999,03148,Bora River Beach, Shirobe Bora 591-1,3,3,9999 
125.257704,24.797368,47214,3,99999,03148,Sunset Beach, Hirara Kugai 643-3,3,3,9999
125.156941,24.857008,47214,3,99999,03148,Sawada Beach,Irabu Sawada,3,3,9999 
125.181135,24.81205,47214,3,99999,03148,Wataguchi Beach,Irabu Town Irabu,3,3,9999

Original data and splitting program​

Download location for the original data​

Shapefile to CSV conversion​

  • Convert using OGR2OGR

Notes​

  • OGR2OGR:
    • ogr2ogr is a vector data conversion tool included in GDAL, a well-known open-source GIS toolset.
    • For Windows, pre-compiled binaries are available at gisinternals.com, as described here.
      • Installation/Windows
        • Stable Releases　⇒ MSVC 2017 x64 (other compilation environments are also supported) ⇒ Generic installer for the GDAL core components (gdal-*-core.msi)
      • How to run ogr2ogr / Windows
        • Windows Menu ⇒ All Apps ⇒ GDAL ⇒ GDAL * Run in the command prompt launched via Command Prompt.
  • CSV header row:
    • The header row of the National Land Numerical Information consists of mechanically assigned numbers (such as P27_001). It will be easier to understand if you refer to the explanation of the attribute information in the National Land Numerical Information and rewrite the CSV header row with feature names before tile division.

CSV Tiling​

tiling1.html​

  • There are no significant differences from the HTML in Tutorial 6.
<!DOCTYPE html> 
<html> 
<title>SVGMapLevel0.1-Rev14-Draft Tutorial2 Coastline & Air Port</title> 
<!-- Viewport: Definition that the display area is the entire screen --> 
<meta name="viewport" content="width=device-width,user-scalable=no,initial-scale=1.0,maximum-scale=1.0" /> 
<meta charset="UTF-8"> 
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 

<!-- Load the SVGMap core API --> 
<script type="module"> 
  import { svgMap } from 'https://cdn.jsdelivr.net/gh/svgmap/svgmapjs@latest/SVGMapLv0.1_r18module.js'; 
  window.svgMap=svgMap 
</script> 

<!-- Load the layer list UI stylesheet --> 
<link href="./js/layerListStyle.css" rel="stylesheet" type="text/css"> 

<body bgcolor="#ffffff" style="overflow:hidden;" > 
<!-- Loading a container file (Container.svg) containing multiple map SVG files (layers) --> 
 <div id="mapcanvas" data-src="Container.svg"></div> 
 <div id="gui"> 
<!-- Zoom up button --> 
  <img id="zoomupButton" style="left: 5px; top: 5px; position: absolute;" src="./img/zoomup.png" onclick="svgMap.zoomup()" width="20" height="20" /> 
<!-- Zoom down button --> 
  <img id="zoomdownButton" style="left: 5px; top: 25px; position: absolute;" <img id="gpsButton" style="left: 5px; top: 45px; position: absolute;" src="./img/gps.png" onclick="svgMap.gps()" width="20" height="20" /> 
<!-- GPS button --> 
  <img id="gpsButton" style="left: 5px; top: 45px; position: absolute;" src="./img/gps.png" onclick="svgMap.gps()" width="20" height="20" /> 
<!-- Title displayed in the upper right corner of the screen --> 
  <font color="blue" style="right: 5px; top: 5px; position: absolute;" >SVGMapLevel0.1 Rev14 Draft : Tutorial2 Coastline & Air Port</font> 
<!-- Displayed in the lower right corner of the screen --> 
  <font color="blue" style="right: 5px; bottom: 5px; position: absolute;" size="-2" >by SVGMap tech.</font> 
<!-- Cross mark displayed in the center --> 
  <img id="centerSight" style="opacity:0.5" src="./img/Xcursor.png" width="15" height="15"/> 
<!-- Latitude and longitude of the crosshair displayed in the lower left corner of the screen (title) --> 
  <font id="posCmt" size="-2" color="brown" style="left: 5px; bottom: 5px; position: absolute;">Lat,Lng:</font> 
<!-- Latitude and longitude displayed as a crosshair in the lower left corner of the screen (initial display of actual values) --> 
  <font id="centerPos" size="-2" color="brown" style="left: 50px; bottom: 5px; position: absolute;" >lat , lng</font> 
<!-- Display of Layer List UI --> 
  <div id="layerList" style="left :30px; top: 10px; width:300px;height:90%; position: absolute; "></div> 
 </div> 
</body> 
</html>

Container.svg​

  • There are no significant differences from the HTML in Tutorial 6.
    • Since GeoJSON data is vector tile data, the class attribute is specified as clickable.
<?xml version="1.0" encoding="UTF-8"?> 
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="122.9800817, -45.398095, 21.97626, 21.0533039" > 
 <globalCoordinateSystem srsName="http://purl.org/crs/84" transform="matrix(1,0,0,-1,0,0)" /> 

<!-- Load OpenStretMap background map as display state --> 
<animation xlink:href="./dynamicOSM_r11.svg" x="-3000" y="-3000" width="6000" height="6000" title="Japan Coastline" class="basemap" visibility="visible"/> 

<!-- Imports tile data from a Point CSV file of Japanese public facility data as the display state --> 
<animation xlink:href="simpleTiling.svg" x="-3000" y="-3000" width="6000" height="6000" title="Cultural Facility" class="POI clickable" visibility="visible"/> 
</svg>

simpleTiling.svg​

  • The icon is defined using the defs element.
  • The actual data is not located here; it is dynamically generated in the web application.
  • Within the group with id="mapTiles", a subgroup is created for each tile, and icons (Points) are placed within that subgroup.
<?xml version="1.0" encoding="UTF-8"?> 
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="-42.8202042942663, -49.9999999999999, 513.842451531196, 600" property="" data-controller="simpleTiling.html#exec=appearOnLayerLoad"> 
<defs> 
<g id="p0"> 
  <circle cx="0" cy="0" r="5" fill="blue"/> 
</g> 
</defs> 
<globalCoSystem srsName="http://purl.org/crs/84" transform="matrix(100,0,0,-100,0,0)" /> 
<g id="mapTiles"> 
</g> 
</svg>

simpleTiling.html, simpleTiling.js​

  • A web app that can be linked to simpleTiling.svg and control its DOM.
  • system dynamically loads GeoJSON data that has been tiled according to the display area. This is similar to Tutorial 5.
  • Since it doesn't have a pyramidal structure that scales down, this tutorial is simpler.
  • Instead, because loading too much data would be required at a small scale (reduced display), the data is not loaded, the rendering is cleared, removeAllTiles() and a message prompting zooming in is displayed on the webApp window.
  • addEventListener("zoomPanMap",zpmFunc) When scaling scroll occurs, call zpmFunc().
  • zpmFunc() Selects and displays tiles to load based on the display area.
  • svgMap.getGeoViewBox() Get geographical display area
  • getTileList(geoViewBox) List the tiles to be displayed.
  • delete tiles[tileKey] Delete groups of tiles that are outside the display area.
  • await loadCSV() Load the tile data (CSV) to be displayed, excluding those already loaded.
  • drawTiles(): Displays the loaded CSV data
  • Create a group to display tiles
  • csv2geojson Generate geoJSON from the imported CSV file.
  • svgMapGIStool.drawGeoJson() Generate an SVG DOM from geoJSON.
  • svgMap.refreshScreen() If the DOM needs to be redrawn at a time other than during scaling/scrolling, you must explicitly request a redraw.
  • Reference information
<!doctype html> 
<html> 
<head> 
<title>Simple Tiling Tutorial</title> 
<meta charset="utf-8"></meta> 
</head> 
<script src="https://cdn.jsdelivr.net/gh/svgmap/svgmapjs@latest/svgMapLayerLib.js"></script> 
<script src="simpleTiling.js"></script> 
<body> 
<h3>Displaying CSV Tile Data</h3> 
<div id="message">-</div> 
</body> 
</html>
addEventListener("load",init); 
addEventListener("zoomPanMap",zpmFunc); 

var latCol=10; 
var lngCol=9; 
var tilesTh=8; // Threshold for the number of tiles that fit on the screen (prevents the system from becoming too slow when zooming out due to too many tiles being loaded) 

function init(){ 
	zpmFunc(); 
} 

function getTileList(geoViewBox){ 
	var tileNames={}; 
	for ( var ty = Math.floor(geoViewBox.y) ; ty<= Math.floor(geoViewBox.y+geoViewBox.height) ; ty++){ 
		for ( var tx = Math.floor(geoViewBox.x) ; tx <= Math.floor(geoViewBox.x+geoViewBox.width) ; tx++){ 
			var tile="tile_" + tx + "_" + ty; 
		} 
	} 
	return ( tileNames); 
			} 
var 
tiles={}; // Variable to store data (CSV as an array) for each tile 
async function zpmFunc(){ 
	var geoViewBox = svgMap.getGeoViewBox(); 
	var tileList=getTileList(geoViewBox); 
	if (Object.keys(tileList).length < tilesTh ){ 
		for ( var tileKey in tiles ){ // Delete unnecessary data 
			if ( !tileList[tileKey]){ 
				delete tiles[tileKey]; 
			} 
		} 
		for ( var tileKey in tileList ){ // Load missing data 
			if ( !tiles[tileKey] ){ 
				tiles[tileKey]=await loadCSV(`tiles/${tileKey}.csv`); // Template literal 
			} 
		} 
		message.innerText="-"; 
		drawTiles(tileList); 
	} else { 
		message.innerText="Too many tiles, Please zoom in."; 
		removeAllTiles(); 
	} 
} 
function removeAllTiles(){ 
	tiles={}; 
	var groups = svgImage.getElementById("mapTiles").children; 
	for ( var i = groups.length -1 ; i >= 0 ; i-- ){ 
		groups[i].remove(); 
	} 
	svgMap.refreshScreen(); 
} 
function drawTiles(tileList){ 
	// tileList: Associative array of tile keys (IDs) to display 
	var tileGroup = svgImage.getElementById("mapTiles"); 
	var groups = tileGroup.children; 
	for ( var i = groups.length -1 ; i >= 0 ; i-- ){ 
		var groupKey = groups[i].getAttribute("id"); 
		if ( !tileList[groupKey]){ 
			groups[i].remove(); // Remove groups that do not need to be displayed 
		} else { 
			delete tileList[groupKey]; // Remove from tileList as it has already been drawn 
		} 
	} 
	// tileList is now a list of tiles to be drawn 
	for ( var tileKey in tileList){ 
		var grp = svgImage.createElement("g"); 
		grp.setAttribute("id",tileKey); 
		tileGroup.appendChild(grp); 
		if ( tiles[tileKey] ){ 
			var geoJson = csv2geojson(tiles[tileKey], lngCol, latCol); 
			svgMapGIStool.drawGeoJson(geoJson, layerID, "",0, "", "p0", "poi", "", grp); 
		}


	


		
	} 
	svgMap.refreshScreen(); 
} 

var schema; 

async function loadCSV(url){ 
	var response = await fetch(url); 
	if ( response.ok ){ 
		var txt = await response.text(); 
		txt=txt.split("\n"); 
		var csv=[]; 
		var schemaLine = true; 
		for ( line of txt){ 
			line = line.trim(); 
			if ( schemaLine ){ 
				schema = line; 
				svgImage.documentElement.setAttribute("property",schema); 
			} else { 
				if ( line !=""){ 
					line=line.split(","); 
					csv.push(line); 
				} 
			} 
			schemaLine = false; 
		} 
		return ( csv ); 
	} else { 
		return ( null ); 
	} 
} 

function csv2geojson(csvArray, lngCol, latCol){ 
	var geoJson = {type: "FeatureCollection", features: []} 
	for ( var csvRecord of csvArray){ 
		var lng = Number(csvRecord[lngCol]); 
		var lat = Number(csvRecord[latCol]); 
		var feature = { type: "Feature", 
			geometry: { 
				type: "Point", 
				"coordinates": [lng, lat] 
			}, 
			"properties": { 
				"csvMetadata": csvRecord.toString() // This process is very rough. 
			} 
		} 
		geoJson.features.push(feature); 
	} 
	return(geoJson); 
}